A touch sensor is a detecting element or system. Direct contact between the touch sensor and an object to be detected induces a physical effect by which the condition of contact and physical properties on the surface of the object to be detected can be identified. The touch sensor shows a very wide range of application. For example, a single touch sensor can serve as a switch, and a two-dimensional touch sensor may provide a tactile image. In an example of application in robots, the touch sensor can be used to control the movement of the robots, such as gripping an object, and is a necessary sensor for motion control. In an example of application in computer field, the touch sensor, when combined with a display, provides a touch controlled input device, which is often referred to as a touch panel, and is widely applied in electronic products of household, communication, and information appliances, such as serving as input interfaces for widely used commercial products of personal digital assistants (PDA's), various household electrical appliances, and game machines. Through combination of the touch sensor and a display, an input interface allows a user to use a finger or a stylus to do selection and input of instruction, according to the image displayed on the display, to the for example PDA's, various household electrical appliances, and game machines, and this use can be further expanded to public information consultation devices, to provide an operation system that improves convenience of use for the public.
The touch sensor has two major types, namely digital touch sensor and analog touch sensor. The digital touch sensor has a touch surface that is divided into a plurality of discrete portions, each of which generates a signal upon touched. Consequently, detection resolution of the digital touch sensor is limited to only recognize the specific discrete portions where a finger or a stylus touches. On the contrary, the analog touch sensor provides a non-discrete signal and thus the detection resolution is only restricted by the overall sensitivity of the analog touch sensor and an electronic circuit that provides control of the touch sensor.
Further, the digital touch sensor and the analog touch sensor are alternatively classified as resistive touch sensor, capacitive touch sensor, sound wave touch sensor, and optic touch sensor. Touch detection techniques that are most commonly used in the touch sensor are resistive touch sensing and capacitive touch sensing.
The capacitive touch sensor comprises a resistive coating layer directly deposited on a solid-state insulation substrate. The insulation substrate is often made of glass and has corners on which electrodes are mounted to establish an electric field. A controller is connected to all electrodes to monitor the electrical current flowing through the electrodes. When a human finger or a touching object forms capacitive coupling with the electrodes, the coupling induces a small current flowing the resistive coating layer and each electrode. Through capacitive coupling between human body and grounding, a path allowing the current to return to the controller is formed. The controller may then determine the coordination of the location of touch according to the current flowing through the electrodes.
The resistive touch sensor comprises a flexible film arranged above a substrate. The flexible film and the substrate are coated with transparent conductive layers and a plurality of insulation spacers are set between the flexible film and the substrate. When an operator touches the flexible film, the flexible film is caused to contact the transparent conductive layer of the substrate, whereby the touching operation causes a current flowing between the film and the substrate. A controller is provided to compare current flows induced in various electrodes or buses printed on each conductive surface in order to determine the location of contact between the film and the substrate.